1. Field of the Invention:
The present invention relates generally to filters and their manufacture. It is particularly useful in increasing and extending the functional utility of air filters such as disposable vacuum cleaner bags, and it will therefore be described for example as it applies to these bags.
2. Description of the Prior Art:
Several products are available that let the users of vacuum cleaners add a more pleasant scent to the air that is filtered by their vacuum cleaners. All such products operate by means of adding a solid inclusion into the vacuum cleaner's dirt receptacle bag, whether by means of the users' placement of a perfume-impregnated tablet or strip directly into the bag, or by operating the vacuum so as to pull such a product or a perfumed powder into the bag. The extra expense and inconvenience of use of these products could be avoided if the disposable filter paper vacuum cleaner bags in most common use today could themselves be made to carry and dispense these perfumes or other active ingredients whose effects were desired by the user.
Previous efforts to develop disposable vacuum cleaner bags which would dispense such active ingredients as perfumes or reodorants into filtered effluents such as air have apparently encountered at least two difficulties: the requirement that the effective action of the active ingredients must be sustained over extended periods of time, and the unacceptably high expenses involved in uniformly applying the requisite high saturation levels of expensive active ingredients throughout the filter, or the expense of treating these ingredients in a manner that would acceptably prolong their effectiveness.
Others have shown how uniform application of a variety of chemical impregnation or polymer film treatments to the filter materials used in vacuum cleaner bags can improve the dust retention of the filter without increasing, or even reducing, the air resistance of the filter. Examples include U.S. Pat. Nos. 1,570,138, issued Jan. 19, 1926 to Gat; 2,251,252, issued to Lovell; 2,698,671, issued Jan. 4, 1955 to Kennette and Sumner; and published German Patent Application 2,940,712, dated Apr. 4, 1981, by Pfennig. U.S. Pat. No. 3,369,348, issued Feb. 20, 1968 to Davis, mentions that a vacuum cleaner's filter may be uniformly impregnated with chemicals to neutralize odors or irritants such as acidic particles which might be present as contaminants in the air which is filtered. U.S. Pat. Nos. 2,848,062 and 2,848,063, issued Aug. 19, 1958 to Meyerhoefer, shows how the air entering a vacuum cleaner bag has directional characteristics that may puncture or abrade specific portions of the interior surface of such a bag, and shows how abrasion-resistant, filtration-reducing barriers may be chemically or mechanically applied selectively to those portions of the interior of the bag most likely to be weakened, in order to extend its useful life. Other somewhat related prior art includes U.S. Pat. Nos. 4,116,648, issued Sept. 26, 1978 to Busch; 4,229,193, issued Oct. 21, 1980 to Miller; 4,749,386, issued June 7, 1988 to Strohmeyer et al. and published German Patent Application 2,835,260, dated Feb. 14, 1980 by Fischer.
None of these devices or teachings of prior art overcome the problems of extended filter ingredient durability and excessive expense discussed above, nor do they deal with economical methods of application or ingredient formulation.